Here is a recipe for using encrypted boot on a Fedora Server system that does not have a monitor or keyboard attached during normal use.

I’ll use Fedora 21 Server, and will have a dedicated encrypted volume group for data but leave the main operating system volume group unencrypted. The encryption key will be stored on a USB memory stick. When it is connected the system will boot normally; otherwise it will wait for a while for it to be connected and finally fall back to emergency mode.

The idea is to make it work a bit more like the Printing screen in the GNOME Settings application. To make any changes you need to click Unlock first, and this fetches all the permissions you need in order to make any changes.

It’s nearly two years since I wrote about session printing, in which the user doesn’t need to modify a locally running CUPS instance in order to print to a network printer. The main advantage of having printing running entirely in the user session is that no special privileges are needed. After all, all you need to do is send the document over the network.

Wanted to write this up in case someone else is scratching their head with the same issue.

Some routers are able to use both 2.4 GHz and 5 GHz frequencies, allowing devices to appear as though they are on the same network regardless of which they use. These actually provide two different wireless networks, with different SSIDs, and bridge between the two.

This works fine for most things, but today I realised that it’s the cause of a printer problem I’d been having. The printer was using the 2.4 GHz network while my laptop was using the 5 GHz one. When I tried to print, the mDNS name of the printer was needed so a multicast query was sent… but the printer didn’t respond.

The reason is the printer never received the query. The mDNS multicast address is 224.0.0.251, which is for multicast to the local subnet only. My router interprets this to mean that packets sent on the 2.4 GHz network will not reach the 5 GHz network.